This invention relates to a method of applying a sealing agent (or sealant) for the purposes of insulation and moistureproofing in the process of manufacturing electronic substrates. More particularly, the present invention relates to a method of applying a sealing agent adapted to seal the end face of the glass substrates of a plasma display to be put together.
U.S. Pat. No. 5,800,614 discloses a device for applying adhesive to platens of a textile screen printing machine as the platens move from the unload stage to the load stage. The device comprises a frame mountable to the screen printing machine so that it extends over the moving platens, at least one interconnectable housing carried by the frame. Each housing has an array of adhesive-depositing nozzles and adhesive-spreading air nozzles plus a drying nozzle. As a platen passes under the housings, a sensor initiates the array of adhesive nozzles to deposit columns of adhesive onto the platens. Then the air nozzles spread the columns of adhesive by blowing air onto the columns. Finally, the spread adhesive is dried by gas from the drying nozzle, preferably directing a single curtain of air under pressure onto the adhesive.
U.S. Pat. No. 5,114,752 discloses a method for depositing liquid material onto a workpiece in the form of a deposit having a desired conformation wherein the material is discharged under pressure from the nozzle of a dispensing gun which can be manipulated by a robot to lay the deposit according to a programmed pattern on the workpiece. One or more gas jets are directed toward the material after the material is discharged from the nozzle to impart a desired conformation to the material deposited on the workpiece. The flow rate of the gas jets is controlled in accordance with liquid flow rate to maintain substantial uniformity of the conformation of the deposit.
U.S. Pat. No. 4,786,060 describes a method for applying liquid sealant in holes of a structural member prior to installing fasteners in such holes, which compromises mixing air with a liquid sealant, spraying a controlled amount of the resulting air-sealant mixture into the holes and depositing liquid sealant therein, and impinging an elevated pressure air stream on the deposited liquid sealant to spread the sealant out and produce a thin layer of sealant in the holes.
GB-1 299 598 describes a method of making a hard brittle rod of resin. A resin is extruded under low pressure through a series of nozzles producing rods of molten resin. These rods are fed on to a moving conveyor belt and passed under the series of sprays from a sprayer which quickly cools the resin by means of a cooling medium which is normally water. The rod is then subjected to a jet or blast of air, preferably hot air from a blower, to remove service moisture.
A known method of the above identified category will be described by way of the process of manufacturing a plasma display. A plasma display is adapted to generate ultraviolet rays by means of electric discharge in gas between a pair of electrodes, irradiating a fluorescent member thereof with the generated ultraviolet rays to generate visible light. The plasma display typically has a sandwich-like layered structure in which various kinds of functional thin films are formed between a front glass and a rear glass, including electrode films, a fluorescent film and ribs for holding the fluorescent film. After bonding lead wires to the electrodes for electric energization, the end face of the combined glass substrates are sealed by means of a sealing agent mainly for the purposes of insulation and moistureproofing.
That structure is outlined in FIG. 2. FIG. 2 is a schematic perspective view showing the portion of a plasma display where a sealing agent is applied and FIG. 3 is a schematic cross sectional view of the portion of a plasma display where the sealing agent is applied. In FIGS. 2 and 3, the plasma display 1 comprises a front glass 2, a rear glass 3 and various kinds of functional thin films 4 arranged between the glass plates, including electrode films, a fluorescent film and ribs for holding the fluorescent film. Thus, the plasma display 1 has a layered structure like that of a sandwich. Reference numeral 5 in FIGS. 2 and 3 denotes a drive substrate for driving the plasma display 1. A large number of thin lead wires 6 are arranged in a film state to connect the drive substrate 5 and the electrodes formed in the functional films 4 of the plasma display 1.
It should be noted that the front glass 2 is dimensionally smaller than the rear glass 3 while the functional films 4 are dimensionally smaller than the front glass 2. After bonding the lead wires 6 to the electrodes of the plasma display 1, a sealing agent 7 is applied to the entire end face of the front glass 2 and the functional films 4 laid on the rear glass 3, including the connecting area of the lead wires 6, in order to seal the plasma display for the purposes of insulation and moistureproofing. Accordingly, as clearly seen in FIG. 2, the shape of the portion to which the sealing agent 7 is applied has an indentation formed between the front glass 2 and the rear glass 3. Referring to FIG. 3, the functional films 4 have a total thickness a that is between 100 and 400 xcexcm and the front glass 2 projects from the functional films 4 by a distance b that is between 500 and 3,000 xcexcm. Thus, the indentation is defined by the thickness a and the distance b.
The aforementioned known method has a drawback as described below. When manufacturing plasma displays of the above described type, there often occur occasions where the indentation ends up without being filled with the applied sealing agent 7 to leave a void (denoted by c in FIG. 3) because the end face of the functional films 4 is located inside that of the front glass 2 on manufacturing considerations.
The sealing agent 7 is typically of the silicon type or of the epoxy type that can be set by ultraviolet rays or heat and shows a viscosity between 100 and 1,000 poise/20 C. When the sealing agent is applied by using an application nozzle directed perpendicularly to the substrate to produce continuous beads of the agent, the indentation may cause a void. While this problem may be avoided by using a low viscosity sealing agent obtained by dissolving the agent into solvent, the gas produced as a result of evaporation of the solvent can contaminate the environment to give rise to a pollution problem. Therefore, there is a demand for the improvement in the sealing.
In view of the above problems, it is therefore the object of the present invention to provide a method of applying a sealing agent to the end face of a laminated substrate such as electronic substrates, in which the indentation or the stepped area formed along the end face can effectively be filled with the sealing agent, i.e., the sealing agent can be improved in throwing power or entering properties.
According to the present invention, the above mentioned object is achieved by a method of applying a sealing agent to a target region, which comprises the steps of: first applying the sealing agent to the target area in the form of successive beads; and then causing a stream of compressed gas from a gas ejecting nozzle to impinge upon said successive beads of the sealing agent as applied, while scanning said successive beads of the sealing agent with said gas ejecting nozzle; the sealing agent is applied to the end face of a substrate, in which an indentation or stepped area is formed along the end face; and the beads of the sealing agent are crushed under the pressure of the gas and spread over the face so that the sealing agent is filled into the indentation or stepped area along the end face.
Thus according to the invention, a sealing agent is applied to a target region in the form of successive beads, and then a stream of compressed gas is blown out of a gas ejecting nozzle while scanning the beads as applied, thereby crushing the beads of the sealing agent and spreading over the face so as to effectively fill the indentation or the stepped area formed along the end face.